This invention relates to a dielectric ceramic material and more particularly, to a dielectric ceramic material suitable for forming resonators designed to operate in the microwave frequencies. It also relates to a method for preparing the same.
To meet the current drastically increasing demand for mobile radio communications, it is strongly required to reduce the size of equipment used therefor. In such communications, filters, diplexers and other circuits including resonator elements are used for frequency selection. The resonators must be reduced in size before the size reduction requirement of communication equipment can be met. The resonators consist of dielectric elements. Since the size of dielectric resonators is in inverse proportion to the square root of the dielectric constant of dielectric materials, a material having a greater dielectric constant must be found in order to enable size reduction of resonators. A shift of service frequency toward a higher frequency requires to increase the packing density of parts, which in turn, requires further size reduction. There are some attempts to form circuits from multilayer dielectric substrates.
Under the circumstances, the dielectric materials have to meet not only conventional requirements including a high dielectric constant in the microwave frequencies and a low temperature coefficient .tau.f of resonance frequency, but also be co-firable with conductors. Among prior art microwave dielectric materials, Ba(Mg.sub.1/3 Ta.sub.2/3)O.sub.3 and Ba(Zn.sub.1/3 Ta.sub.2/3)O.sub.3 are known to have a high dielectric constant in the microwave frequencies. However, since these microwave dielectric materials including Ba(Mg.sub.1/3 Ta.sub.2/3)O.sub.3 and Ba(Zn.sub.1/3 Ta.sub.2/3)O.sub.3 have a firing temperature as high as about 1,300.degree. C., it is difficult to achieve fine or complex networks of conductor when the dielectric material is co-fired with the conductor. Inversely, those dielectric materials having a lower firing temperature have a low dielectric constant, for example, a (glass +TiO.sub.2) system having a dielectric constant of about 10.